K88-79

I have flat top piston's for my 350 build and I thought I needed a thin head gasket to up compression since my motor is the low comp 79 z28 shorty .....but the guy at autozone told me that a thin head gasket would be pointless??? If he's not right.. what size should I use?

79 350 from z28
Trw flat tops
Comp cam 284 dur 481 lift
291 camel humps (for now)
Edelbrock performer air gap
Q-jet 750
Headers
Dual exhaust
Posi

AlkyIROC

Nothing wrong with using a thin head gasket. How thin depends on what type of gasket you want to use. The aftermarket composite gaskets are actually thick. A MLS gasket which is the best way to go is very thick. The factory used a thin steel head gasket for many years and is the thinnest you can go. I believe the factory steel gasket is only 0.018".

Using a thin head gasket means the valves are also closer to the pistons. You should check the piston to valve clearance with the new gasket before firing up the engine. Pushrod geometry should also be checked.

K88-79

So a thin head gasket isn't necessary for upping compression with my flat tops?? I'm asking cause someone said flat top piston's without a thin head gasket was a waste.

AlkyIROC

Depends on the combustion chamber size in the heads and what the compression ratio is with different thickness head gaskets.

K88-79

63cc on heads

AlkyIROC

Find the different gasket thicknesses and do the calculations to get the compression ratio you desire.

http://www.wallaceracing.com/cr_test2.php

ASE doc

With a common head gasket such as the Felpro Permatorque, you will be right at 10:1 CR. Assuming that your flat tops are the common 4 eye brow valve relief type. That's about right for your cam. The Permatorque will provide much better sealing and a longer service life than the thin steel.

K88-79

Thanks guys

DENN_SHAH

iTrader: (1)

in addtion to whats been said, there is something more important than compression that you need to take into consideration before choosing the head gaskets, the quench.
you want quench to be around .040~0.050.
if the pistons are at zero deck height and you use a thin shim gasket, the pistons will be too close to the heads.
too much quench and you'll have detonation problems.

86LG4Bird

iTrader: (1)

..finally, somebody mentioned quench.....THE major advantage of decking a block or running a thin gasket!
Tighten it down to .030-.035" (assuming hyper pistons, close bore fit, and minimal piston rock at TDC). Reduced quench clearance will always allow your engine to tolerate more compression because of the low rpm mixture motion that the quench/squish provides.
Unless your block has been decked where the pistons are less than .015 in the hole, run the Felpro 1094 rubber coated .015" shim gasket.

Ps. Don't worry much about what your typical guy at Autozone says!

Sparkytfl

I dont see any mention of sealing problems and whether or not the heads and block were surfaced to be totally flat.

K88-79

Cool...I appreciate all the info.

86LG4Bird

iTrader: (1)

Good you pointed that out. I was assuming with his rebuild that all of that was guaranteed.
With that being said, I've used the coated .015 shim gaskets on "re-assembles", not necessarily rebuilds, without resurfacing, with never any problems. Just checked deck and heads for flatness.